Imaging technique performing focusing on plurality of images

ABSTRACT

A focusing technique detects motion vectors of a plurality of images, combines the images in accordance with the detected motion vectors, extracts a signal corresponding to a focusing state of a lens unit with respect to a subject, and controls the lens unit in accordance with the extracted signal to perform focusing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging technique and in particular,to an imaging technique performing focusing.

2. Description of the Related Art

Digital video cameras, or digital camcorders, which form an image of asubject on a semiconductor imaging device, such as a two-dimensionalcharge-coupled device (CCD) image sensor, by means of an optical imagingsystem, convert the image into an electrical signal, and record imagedata of moving images obtained on a record medium, such as asemiconductor memory, a magnetic disk, or a magnetic tape, and digitalstill cameras capable of recording moving images in addition to stillimages are becoming popular. For current digital video cameras anddigital still cameras, all important tasks in image capturing, such asexposure settings, focusing, and the like, are automated, so that evenusers who are inexperienced at camera operations seldom fail to captureimages properly.

CCD image sensors, as mentioned above, have the electronic shuttercapability that allows a user to freely set a shutter speed. Therefore,a user can adjust the exposure time in accordance with the motion of asubject or illumination conditions. For example, for capturing a movingimage of a subject in dark conditions, due to the low illumination, auser selects a low speed setting so as to make an electronic shutterspeed lower in order to have an increased exposure. This shutter speedis slower than a normal shutter speed of 1/60 second in one field of avideo signal, for example, 1/30 sec. or 1/15 sec. However, slow shutterspeeds cause image capturing to be susceptible to the effects of camerashaking, and therefore, an image of a subject is blurred. To preventthis, a method is proposed in which an image capturing operation with anexposure time that does not cause motion blurring is performed multipletimes and the obtained images are combined while their displacements arecorrected, thereby realizing a resulting image with a long exposure time(see, for example, Japanese Patent No. 3110797).

Japanese Patent No. 3110797 discloses an apparatus for combiningcaptured images. The apparatus includes a detecting unit for detectinginformation regarding motion between a plurality of images and an imagemoving unit for transforming the positions of the plurality of images ina plane coordinate system in accordance with the detected information.With the application of this technique, in a case when a moving image ofa subject in dark conditions requiring a low-speed shutter setting forsufficient exposure is to be captured, an exposure time that does notcause an image to be affected by camera shaking, for example, a normalspeed of 1/60 sec. in one field of a video signal is set, instead of anormal low-speed shutter setting of 1/30 sec., 1/15 sec., or a slowertime, an image capturing operation is performed multiple times in unitsof 1/60 sec. for a period of time equal to an exposure period of alow-speed shutter, and the plurality of images obtained are combined, sothat moving images that have exposure amounts equal to that of alow-speed shutter and that are not affected by camera shaking can beacquired in units of the same time period as an exposure time of thelow-speed shutter.

However, the method for setting an exposure time that does not cause animage to be affected by camera shaking, instead of selecting a low-speedshutter setting, for capturing an image multiple times in a period oftime equal to an exposure period of a low-speed shutter, and forcombining the plurality of images captured in order to acquire movingimages that do not suffer the effects of camera shaking and that havethe same exposure as that of the low-speed shutter setting, as describedabove, significantly affects a focus performance in an automaticfocusing unit. Specifically, a normal focusing unit for processingmoving images performs focusing by a method (so-called “televisionautofocus (TV-AF) method”) for extracting a definition signal forfocusing from a signal obtained from a signal output from an imagingdevice every image capturing in accordance with a focusing state of thelens unit and controlling a lens unit using the definition signal suchthat, for example, the amount of definition signal is maximized.However, when a moving image of a subject in dark conditions, due to thelow illumination, is captured, an amplitude of a signal output from theimaging device at intervals of multiple image capturing operations istoo small, and as a result, an amplitude of a definition signal forfocusing obtained from the imaging device is too small. In other words,the obtained signal is inadequate to realize a sufficient focusperformance (low-contrast conditions).

FIG. 4 shows the amount of signal stored in the imaging device, theamount of signal output from the imaging device, and the amplitude ofthe definition signal obtained from the output from the imaging devicein this case. In FIG. 4, chart (3-1) represents the relationship betweenthe amount of signal stored in the imaging device and an exposureperiod. Reference numerals e2, o3, e3, . . . individually representrepeat numbers of even or odd fields in the exposure period in theimaging device. Since a resulting moving image is not affected by camerashaking and has an exposure equal to that of a low-speed shutter settingdue to processing of an image combining unit disposed at a subsequentstage even when an image of a subject in the dark is captured, anexposure period, T, is set to the order of 1/60 sec., and thus a signalis read every 1/60 sec., as shown in chart (3-2). Combining signals offour reading operations realizes an image (composite image) with anexposure equal to an exposure time of 1/15 sec. of a low-speed shuttersetting. However, the amount of definition signal extracted is small inaccordance with the amount of signal stored in the imaging device, asshown in chart (3-3), and therefore, the extracted definition signal isinadequate to realize a sufficient focus performance.

Charts (3-4), (3-5), and (3-6) represent the amount of signal stored inthe imaging device, the amount of signal output from the imaging device,and the amplitude of the definition signal obtained from the output fromthe imaging device, respectively, when a normal low-speed shuttersetting of 1/15 sec. is selected as an exposure period. In this case,although the amplitude of the definition signal is large, the outputfrom the imaging device, i.e., the definition signal has many remainingcomponents leading to poor contrast because of a long exposure. Thiscauses degradation in focus performance.

If, for example, image combining processing, as described above, is notperformed, in a case when an image of a subject in the dark is captured,an amplitude of the definition signal can be amplified by increasing thegain of a signal that is output from the imaging device every a normalspeed of 1/60 sec. in one field of a video signal and that has a smallamplitude, thus realizing an image with contrast, albeit with muchnoise. However, since this method amplifies the amplitude of a signaloutput from the imaging device and increases an apparent exposure, ahigh-quality moving image with less noise is not acquired.

SUMMARY OF THE INVENTION

The present invention provides a technique capable of preventingdegradation in focus performance of an autofocus operation whenacquiring moving images with no effect of camera shaking by a method forcombining a plurality of images.

According to a first aspect of the present invention, an imagingapparatus includes a solid-state imaging unit, a detecting unit, acombining unit, an extracting unit, and a focus controlling unit. Thesolid-state imaging unit is configured to receive an image of a subjectformed through a lens unit configured to perform focusing and to outputan image signal composed of a plurality of continuous images. Thedetecting unit is configured to detect a motion vector of each of theplurality of images. The combining unit is configured to combine theplurality of images in accordance with each motion vector detected bythe detecting unit to produce a composite image. The extracting unitconfigured to extract a first signal corresponding to a focusing stateof the lens unit with respect to the subject in accordance with thecomposite image. The focus controlling unit configured to control thelens unit in accordance with the extracted first signal to performfocusing.

Correcting displacement components of a plurality of continuous imagesand combining the images suppress the effects of camera shaking when amoving image is captured with a low-speed shutter setting, thusimproving precision of the captured moving image. Additionally,extracting a definition signal from a composite image and performingfocusing using the definition signal enhance a focus performance when amoving image of a subject in dark conditions, due to the lowillumination, is captured.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram of a digital video camera according to atleast one exemplary embodiment of the present invention.

FIG. 2 is a timing chart showing an amplitude of a definition signalaccording to at least one exemplary embodiment of the present invention.

FIG. 3 is a flowchart for control when an anti-shake image combiningsystem is activated according to an embodiment.

FIG. 4 is a timing chart showing an amplitude of a definition signal ina known art.

FIG. 5 is a flowchart for control when the anti-shake image combiningsystem is activated according to another embodiment.

FIG. 6 is a flowchart for control when the anti-shake image combiningsystem is activated according to still another embodiment.

DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention are described below withreference to the drawings.

FIG. 1 shows an example of a digital video camera according to at leastone exemplary embodiment of the present invention. A beam (image capturelight beam) incident from an imaging lens 11 passes through a diaphragm13 a, and the amount of light is adjusted. The beam then passes througha shutter 12 a, and an image is formed in an imaging unit 17. Theimaging unit 17 is composed of a two-dimensional image sensor, such as aCCD.

The imaging lens 11 is composed of a plurality of optical lens groups.These lens groups in whole or in part move along an optical axis 10 witha driving force supplied from an autofocus (AF) driving motor 14 a andperform focusing by stopping at a predetermined in-focus position. TheAF driving motor 14 a is driven by receiving a driving signal from afocus driving unit 14 b. Some of the optical lens groups of the imaginglens 11 move along the optical axis 10 with a driving force from a zoomdriving motor 15 a and change an angle of view in image capturing bystopping at a predetermined zoom position. The zoom driving motor 15 ais driven by receiving a driving signal from a zoom driving unit 15 b.

The diaphragm 13 a includes a plurality of diaphragm blades. Thediaphragm blades are actuated by receiving a driving force from adiaphragm driving unit 13 b so as to change an area (diameter) of anaperture through which light beams pass. The shutter 12 a includes aplurality of shutter blades. The shutter blades are actuated byreceiving a driving force from a shutter driving unit 12 b so as to openor close an aperture though which light beams pass. As a result, theamount of light entering the imaging unit 17 is controlled. The shutter12 a is used when a still picture is captured with the digital videocamera.

Driving an imaging device driving unit 16, the focus driving unit 14 b,the zoom driving unit 15 b, the diaphragm driving unit 13 b, and theshutter driving unit 12 b are controlled by an imaging controller 18.The imaging controller 18 can receive operation signals from a diaphragmoperating unit 13 c, a zoom operating unit 15 c, and an anti-shake imagecombination operating unit 120, which is described below, and supply theoperation signals to the imaging device driving unit 16, the focusdriving unit 14 b, the zoom driving unit 15 b, the diaphragm drivingunit 13 b, and the shutter driving unit 12 b in accordance with imagecapturing conditions so as to determine image capturing settings so thatan image capturing operation is carried out. The diaphragm operatingunit 13 c is not used in normal image capturing since the aperturediameter of the diaphragm 13 a is automatically set in a camera sectionwhen an image is captured. However, the diaphragm operating unit 13 c isprovided in order that a user can optionally determine an imagecapturing setting.

The imaging controller 18 measures the subject brightness (performsmetering) using a metering signal 130 based on an image signal capturedin a signal processing unit 111, which is described below. In accordancewith the obtained measurement, the aperture diameter of the diaphragm 13a and an electronic shutter timing (exposure time) of the imaging devicedriving unit 16 are determined.

A video (image) signal output from the imaging unit 17 is converted fromanalog to digital form by an analog-to-digital (A/D) converting unit 110and input to the signal processing unit 111. The signal processing unit111 performs signal processing, such as formation of luminance signalsand color signals, on an input signal, so as to create a video signalfor color moving images.

A video signal subjected to signal processing in the signal processingunit 111 is input to an image correction unit 117 via a signal switchingunit 112. The image correction unit 117 performs gamma correction,compression, and the like on an input signal.

A signal output from the image correction unit 117 is input to a displayunit 118 and a video recording unit 119, so that a captured moving imageis displayed on the display unit 118 and recorded in the video recordingunit 119.

In the process described above, for a subject to be captured is in darkconditions requiring a long exposure time, there is a possibility that anormal low-speed shutter setting causes image capturing to be affectedby camera shaking. Therefore, a user operates the anti-shake imagecombination operating unit 120 so that an anti-shake image combiningsystem is activated and the processing is switched to an operationdescribed below, as shown in the flowchart of FIG. 3 performed by theimaging controller 18.

In step S301, metering is started. In accordance with the obtainedmeasurement, an electronic-shutter timing (exposure time) of the imagingdevice driving unit 16 and the aperture diameter of the diaphragm 13 aare set. In normal settings, under the above-mentioned condition, inwhich the subject is in the dark, the diaphragm would be set so as to befully open and the exposure time would be set so as to be long. In thisembodiment, however, the long exposure time, which would be set innormal settings, is divided into a plurality of continuous shortexposure time segments such that the total exposure produced by an addoperation carried out in a method for combining a plurality of images,which is described later, is equal to the amount of exposure that wouldbe obtained when a low-speed shutter setting is selected. Imagecapturing with divided short exposure time segments causes underexposurein a single image obtained, but it has little effect of camera shaking.

A plurality of continuous images are combined by add operations at thesame intervals as a cycle of a low-speed shutter setting, so thatresulting moving images with minimized effects of camera shaking andimproved exposure are realized.

An image signal output from the imaging unit 17 is converted to adigital signal by the A/D converting unit 110 and is then subjected tosignal processing by the signal processing unit 111. When the anti-shakeimage combining system is activated by an operation of the anti-shakeimage combination operating unit 120 and information indicating thisreaches the imaging controller 18, image data from the signal processingunit 111 is input to an image storing unit 113 via the signal switchingunit 112 (step S302). The image storing unit 113 includes a storing areawith a storage capacity for storing a plurality of images correspondingto the number of division of exposure time, and stores a plurality ofcaptured images of continuous video fields such that the stored imagesare overwritten in accordance with subsequent input image data. Adisplacement detecting unit 114 extracts a common feature point in theimages stored in the image storing unit 113 and detects a motion vectorof each of the continuous images by calculating the coordinates of thefeature point present in a capturing screen (step S303). A coordinatetransforming unit 115 corrects each of the differences (performscoordinate transformation) in accordance with the coordinates of thefeature point in each of the images so that the positions of the featurepoints in the images are coincided with each other. Specifically, videoimages are sequentially moved by the magnitude of a detected motionvector in a direction opposite to the motion vector. Then, good videoimages in which displacements are corrected are combined bysuperposition in an image combining unit 116 (step S304). As a result,the effects of camera shaking produced in between the fields arecorrected, so that good video signals are acquired.

At the same time, the imaging controller 18 calculates an in-focusposition of the imaging lens 11 in accordance with a definition signalformed by being extracted from a second output 140 for definition signalextraction before image combination from the signal processing unit 111or a first output 150 for definition signal extraction after imagecombination from the image combining unit 116 while driving the focusdriving unit 14 b.

The imaging controller 18 receives the second output 140, which is fordefinition signal extraction before image combination, from the signalprocessing unit 111 and the first output 150, which is for definitionsignal extraction after image combination, from the image combining unit116. The imaging controller 18 compares an amplitude of a definitionsignal created from the second output 140 with a predeterminedthreshold. When the amplitude is smaller than the predeterminedthreshold, like in a case when an image of a subject in dark conditionsis captured, the imaging controller 18 selects the first output 150 as asignal source for extracting a definition signal, not the second output140 (step S305). In accordance with this selected output with a largeamplitude, the imaging controller 18 performs an autofocusing operationusing a hill-climbing method (contrast detection autofocusing) bygenerating an evaluation value of a frequency peak, an evaluation valueof a brightness level peak, and an evaluation value of max-min datawithin a measuring frame whose position and size are determined forautofocusing (step S306).

Since the selection of a source for a definition signal includes anappropriate hysteresis with respect to a threshold, frequent occurrenceof switching the source when the amplitude of the definition signalobtained from the second output 140 lies in a range around the thresholdis suppressed.

FIG. 2 shows the amount of signal stored in the imaging device, theamount of signal output from the imaging device, and the amplitude ofthe definition signal obtained from the output from the imaging device.In FIG. 2, chart (2-1) represents the relationship between the amount ofsignal stored in the imaging device and an exposure period. Referencenumerals e2, o3, e3, . . . individually represent repeat numbers of evenor odd fields in the exposure period in the imaging device. Since aresulting moving image is not affected by camera shaking and that has anexposure equal to that of a low-speed shutter setting due to processingof the image combining unit 116 disposed at a subsequent stage even whenan image of a subject in the dark is captured, an exposure period, T, isset to the order of 1/60 sec. and thus a signal is read every 1/60 sec.,as shown in chart (2-2). Combining signals of four reading operationsrealizes an image (composite image) with an exposure equal to anexposure time of 1/15 sec. of a low-speed shutter setting, as shown inchart (2-3). If the amplitude of a second definition signal is smallerthan a predetermined value, a first definition signal is selected from acomposite image after image combination and therefore the obtaineddefinition signal has a large amplitude and a high signal-to-noiseratio. Thus, high-precision evaluation data for autofocusing isgenerated, as shown in chart (2-4).

As described above, this embodiment includes a lens unit (11) forperforming focusing, a solid-state imaging unit (17) for receiving animage of a subject formed through the lens unit (11) and for outputtingan image signal composed of a plurality of continuous images obtained bypressing an electronic shutter in succession, a detecting unit (114) fordetecting a motion vector between an image of the plurality of imagesand the immediately preceding image with respect to each of theplurality of images, a combining unit (115, 116) for correcting adisplacement of each image in accordance with the corresponding detectedmotion vector detected by the detecting unit (114) and for combining theimages to produce a composite image, an extracting unit (116) forextracting a first definition signal (150) corresponding to a focusingstate of the lens unit (11) with respect to the subject in accordancewith the composite image, and a focus controlling unit (18, 14 a, and 14b) for controlling the lens unit (11) in accordance with the extracteddefinition signal to perform focusing.

The extracting unit (111) extracts a second definition signal (140)corresponding to a focusing state of the lens unit (11) in accordancewith an image before image combination. The focus controlling unit (18,14 a, and 14 b) selects the second definition signal (140) based on theimage before image combination or the first definition signal (150)based on the composite image after image combination, and controls thelens unit (11) in accordance with the selected definition signal toperform focusing.

The focus controlling unit (18) controls the lens unit (11) inaccordance with the second definition signal (140) to perform focusingwhen an amplitude of the second signal (140) is larger than a threshold,and the focus controlling unit (18) controls the lens unit (11) inaccordance with the first signal (150) to perform focusing when theamplitude of the second signal (140) is smaller than the threshold.

Correcting displacement components of a plurality of continuous imagesand combining the images suppress the effects of camera shaking when amoving image is captured with a low-speed shutter setting, thusimproving precision of the captured moving image. Additionally,extracting a definition signal from a composite image and performingfocusing using the definition signal enhance a focus performance when amoving image of a subject in dark conditions, due to the lowillumination, is captured.

An imaging apparatus capable of acquiring a moving image with anexposure equal to that of a low-speed shutter setting and with no effectof camera shaking by a method for combining a plurality of imagesincludes an extracting unit for extracting a definition signal forfocusing from a composite image after video images are corrected andcombined by superposition, in order to prevent degradation in focusperformance of an autofocuing unit.

According to this embodiment, a definition signal for focusing can beextracted from a composite image after video images are corrected andcombined by superposition. Therefore, when a moving image of a subjectin dark conditions, due to the low illumination, is capture, focusingcontrol using a TV-AF method with a composite image that is corrected soas not to be affected by camera shaking and that has an increased signalamplitude and an improved contrast can be realized, and as a result, afocus performance higher than conventional methods can be realized.Additionally, when a moving image is captured with a low-speed shuttersetting, the effects of camera shaking are corrected, thus improvingprecision of captured moving images.

A second embodiment according to a technique for realizing anappropriate focus performance even when an obtained signal is inadequateto attain a sufficient focus performance (low-contrast conditions) isdescribed below. Like the first embodiment described above, the secondembodiment can realize an appropriate focus performance when a movingimage of a subject in dark conditions, due to the low illumination, iscaptured and an amplitude of a definition signal for focusing obtainedfrom the imaging device is small.

The second embodiment has the structure of the digital video camerashown in FIG. 1. This embodiment differs from the first embodiment inthe timing of extracting the definition signal and the usage of theextracted definition signal. This embodiment is described below withreference to the flowchart of FIG. 5, which is controlled by the imagingcontroller 18.

In step S501, metering is started, as in the case of step S301 of FIG.3. In accordance with the obtained measurement, an electronic-shuttertiming (exposure time) of the imaging device driving unit 16 and theaperture diameter of the diaphragm 13 a are set. In normal settings,under the condition in which a subject is in the dark, the diaphragmwould be set so as to be fully open and the exposure time would be setso as to be long. In the second embodiment, however, the exposure iscontrolled by the method for combining a plurality of images, which isdescribed above, as in the case with the first embodiment. This causesunderexposure in a single image obtained.

An image signal output from the imaging unit 17 is converted to adigital signal by the A/D converting unit 110 and is then subjected tosignal processing by the signal processing unit 111. In step S502, as inthe case of step S302, when the anti-shake image combining system isactivated by an operation of the anti-shake image combination operatingunit 120 and information indicating this reaches the imaging controller18, image data from the signal processing unit 111 is input to the imagestoring unit 113 via the signal switching unit 112.

In step S503, as in the case of step S303, the displacement detectingunit 114 extracts a common feature point in the images stored in theimage storing unit 113 and detects a motion vector of each of thecontinuous images by calculating the coordinates of the feature pointpresent in a capturing screen. The coordinate transforming unit 115corrects each of the differences (performs coordinate transformation) inaccordance with the coordinates of the feature point in each of theimages so that the positions of the feature points in the images arecoincided with each other. Specifically, video images are sequentiallymoved by the magnitude of a detected motion vector in a directionopposite to the motion vector. Then, good video images in whichdisplacements are corrected are combined by superposition in the imagecombining unit 116 (step S504). As a result, the effects of camerashaking produced in between the fields are corrected, so that good videosignals are acquired.

At the same time, according to the second embodiment, the imagingcontroller 18 extracts definition signals from the second output 140,which is for definition signal extraction before image combination, fromthe signal processing unit 111 while driving the focus driving unit 14 b(step S510).

Since the brightness level of the obtained image is low, the level of asingle definition signal extracted is low. In step S511, the definitionsignals are added together in accordance with the image combination instep S504 to produce a composite definition signal. In this case, thedefinition signals are added together in accordance with the number ofdivision of the exposure time so that the resulting composite definitionsignal attains a high level. In accordance with the composite definitionsignal, an autofocusing operation using the hill-climbing method(contrast detection autofocusing) is performed (step S512).

The extraction of each of the definition signals in step S510 may becontrolled so that an extraction area for the definition signal iscontrolled in accordance with the result of the detection of the motionvector in step S503. Specifically, the extraction area for thedefinition signal in a video signal is moved in accordance with thedetected motion vector, so that the definition signal is extracted fromthe extraction area corresponding to the images to be combined in stepS504.

As described above, extracting the definition signals from a videosignal prepared before the images are combined and adding the extracteddefinition signals together improves a focus performance when a movingimage of a subject in dark conditions, due to the low illumination, iscaptured.

In the flowchart of FIG. 5, after the motion vector is detected in stepS503, the definition signals are extracted in step S510. However, asshown in FIG. 6, the definition signals may be extracted (step S520) inparallel with the detection of the motion vector and the extracteddefinition signals may be added together (step S521) before the focusingoperation is performed (step S522). In this case, moving the extractionarea for each of the definition signals in accordance with the detectedmotion vector cannot be performed, unlike the second embodimentdescribed above. However, a focus performance when a moving image of asubject in dark conditions, due to the low illumination, is captured isimproved by extracting the definition signals from a video signalprepared before the images are combined and adding the extracteddefinition signals together.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

This application claims priority from Japanese Patent Application No.2004-181074 filed Jun. 18, 2004, which is hereby incorporated byreference herein.

1. An imaging apparatus comprising: a solid-state imaging unitconfigured to receive an image of a subject formed through a lens unitconfigured to perform focusing and to output an image signal composed ofa plurality of continuous images; a detecting unit configured to detecta motion vector of each of the plurality of images; a combining unitconfigured to combine the plurality of images in accordance with eachmotion vector detected by the detecting unit to produce a compositeimage; an extracting unit capable of extracting a first signalcorresponding to a focusing state of the lens unit from the combinedimage, and a second signal corresponding to a focusing state of the lensunit with respect to a subject from the plurality of images before beingcombined; and a focus controlling unit configured to control the lensunit in accordance with the extracted first signal and the second signalto perform focusing.
 2. The imaging apparatus according to claim 1,wherein the extracting unit extracts a second signal corresponding to afocusing state of the lens unit with respect to the subject inaccordance with the images before being combined, and the focuscontrolling unit selects the second signal or the first signal.
 3. Theimaging apparatus according to claim 1, wherein the focus controllingunit controls the lens unit in accordance with the second signal toperform focusing when an amplitude of the second signal is larger than athreshold, and the focus controlling unit controls the lens unit inaccordance with the first signal to perform focusing when the amplitudeof the second signal is smaller than the threshold.
 4. The imagingapparatus according to claim 1, further comprising: a storing unitconfigured to store the image signal composed of the plurality of imagesoutput from the solid-state imaging unit, wherein the combining unitcombines the plurality of images after correcting a displacement of eachof the plurality of images stored in the storing unit.
 5. A method forcontrolling an imaging apparatus including a solid-state imaging unitconfigured to receive an image of a subject formed through a lens unitfor performing focusing and to output an image signal composed of aplurality of continuous images, the method comprising: a detecting stepof detecting a motion vector of each of the plurality of images; acombining step of combining the plurality of images in accordance witheach motion vector detected in the detecting step to produce a compositeimage; an extracting step of extracting a first signal corresponding toa focusing state of the lens unit, wherein the first signal is generatedfrom the composite image; and a focus controlling step of controllingthe lens unit in accordance with the extracted first signal to performfocusing.
 6. An imaging apparatus comprising: a solid-state imaging unitconfigured to receive an image of a subject formed through a lens unitconfigured to perform focusing and to output an image signal composed ofa plurality of continuous images; a combining unit configured to combinethe plurality of images in accordance with a motion vector of theplurality of images; an extracting unit configured to extract firstsignals corresponding to a focusing state of the lens unit with respectto the subject from a signal prepared before the images are combined andconfigured to add the extracted first signals together so as to producea second signal, wherein the first signal is generated from theplurality of images before becoming combined; and a focus controllingunit configured to control the lens unit in accordance with the secondsignal to perform focusing.
 7. A method for controlling an imagingapparatus including a solid-state imaging unit configured to receive animage of a subject formed through a lens unit for performing focusingand to output an image signal composed of a plurality of continuousimages, the method comprising: a combining step of combining theplurality of images in accordance with a motion vector of the pluralityof images; an extracting step of extracting first signals correspondingto a focusing state of the lens unit with respect to the subject from asignal prepared before the images are combined and of adding theextracted first signals together to produce a second signal, wherein thefirst signal is generated from the plurality of images before becomingcombined; and a focus controlling step of controlling the lens unit inaccordance with the second signal to perform focusing.